michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
michael@0:  * vim: set ts=8 sts=4 et sw=4 tw=99:
michael@0:  * This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef jsweakcache_h
michael@0: #define jsweakcache_h
michael@0: 
michael@0: #include "jscntxt.h"
michael@0: #include "gc/Marking.h"
michael@0: #include "js/HashTable.h"
michael@0: #include "vm/Runtime.h"
michael@0: 
michael@0: namespace js {
michael@0: 
michael@0: // A WeakCache is used to map a key to a value similar to an HashMap except
michael@0: // that its entries are garbage collected.  An entry is kept as long as
michael@0: // both the key and value are marked.
michael@0: //
michael@0: // No mark function is provided with this weak container.  However, this weak
michael@0: // container should take part in the sweep phase.
michael@0: template <class Key, class Value,
michael@0:           class HashPolicy = DefaultHasher<Key>,
michael@0:           class AllocPolicy = RuntimeAllocPolicy>
michael@0: class WeakCache : public HashMap<Key, Value, HashPolicy, AllocPolicy> {
michael@0:   private:
michael@0:     typedef HashMap<Key, Value, HashPolicy, AllocPolicy> Base;
michael@0:     typedef typename Base::Range Range;
michael@0:     typedef typename Base::Enum Enum;
michael@0: 
michael@0:   public:
michael@0:     explicit WeakCache(JSRuntime *rt) : Base(rt) { }
michael@0:     explicit WeakCache(JSContext *cx) : Base(cx->runtime()) { }
michael@0: 
michael@0:   public:
michael@0:     // Sweep all entries which have unmarked key or value.
michael@0:     void sweep(FreeOp *fop) {
michael@0:         // Remove all entries whose keys/values remain unmarked.
michael@0:         for (Enum e(*this); !e.empty(); e.popFront()) {
michael@0:             // Checking IsMarked() may update the location of the Key (or Value).
michael@0:             // Pass in a stack local, then manually update the backing heap store.
michael@0:             Key k(e.front().key);
michael@0:             bool isKeyDying = gc::IsAboutToBeFinalized(&k);
michael@0: 
michael@0:             if (isKeyDying || gc::IsAboutToBeFinalized(e.front().value)) {
michael@0:                 e.removeFront();
michael@0:             } else {
michael@0:                 // Potentially update the location of the Key.
michael@0:                 // The Value had its heap addresses correctly passed to IsMarked(),
michael@0:                 // and therefore has already been updated if necessary.
michael@0:                 // e.rekeyFront(k);
michael@0:             }
michael@0:         }
michael@0: 
michael@0: #if DEBUG
michael@0:         // Once we've swept, all remaining edges should stay within the
michael@0:         // known-live part of the graph.
michael@0:         for (Range r = Base::all(); !r.empty(); r.popFront()) {
michael@0:             Key k(r.front().key);
michael@0: 
michael@0:             JS_ASSERT(!gc::IsAboutToBeFinalized(&k));
michael@0:             JS_ASSERT(!gc::IsAboutToBeFinalized(r.front().value));
michael@0: 
michael@0:             // Assert that IsMarked() did not perform relocation.
michael@0:             JS_ASSERT(k == r.front().key);
michael@0:         }
michael@0: #endif
michael@0:     }
michael@0: };
michael@0: 
michael@0: // A WeakValueCache is similar to a WeakCache, except keys are never marked.
michael@0: // This is useful for weak maps where the keys are primitive values such as uint32_t.
michael@0: template <class Key, class Value,
michael@0:           class HashPolicy = DefaultHasher<Key>,
michael@0:           class AllocPolicy = RuntimeAllocPolicy>
michael@0: class WeakValueCache : public HashMap<Key, Value, HashPolicy, AllocPolicy>
michael@0: {
michael@0:   public:
michael@0:     typedef HashMap<Key, Value, HashPolicy, AllocPolicy> Base;
michael@0:     typedef typename Base::Range Range;
michael@0:     typedef typename Base::Enum Enum;
michael@0: 
michael@0:     explicit WeakValueCache(JSRuntime *rt) : Base(rt) { }
michael@0:     explicit WeakValueCache(JSContext *cx) : Base(cx->runtime()) { }
michael@0: 
michael@0:   public:
michael@0:     // Sweep all entries which have unmarked key or value.
michael@0:     void sweep(FreeOp *fop) {
michael@0:         // Remove all entries whose values remain unmarked.
michael@0:         for (Enum e(*this); !e.empty(); e.popFront()) {
michael@0:             if (gc::IsAboutToBeFinalized(e.front().value()))
michael@0:                 e.removeFront();
michael@0:         }
michael@0: 
michael@0: #if DEBUG
michael@0:         // Once we've swept, all remaining edges should stay within the
michael@0:         // known-live part of the graph.
michael@0:         for (Range r = Base::all(); !r.empty(); r.popFront())
michael@0:             JS_ASSERT(!gc::IsAboutToBeFinalized(r.front().value()));
michael@0: #endif
michael@0:     }
michael@0: };
michael@0: 
michael@0: } // namespace js
michael@0: 
michael@0: #endif /* jsweakcache_h */